Rat parotid gland slices in Krebs-Ringer bicarbonate medium secrete amylase and DNase at an enhanced rate in response to epinephrine. A high potassium concentration (60 m M) effectively replaced epinephrine as a stimulant of secretion. The process was dependent on oxygen, was inhibited by DNP and cyanide, but not by inhibitors of glycolysis. When epinephrine was the stimulant, secretion was also dependent on a minimal concentration of potassium (5 m M). Slices lost 90% of their potassium content in 75 minutes when incubated in a medium free of this ion. Once exhausted of potassium the slices no longer showed enhanced enzyme secretion when epinephrine was added. Other ions of the Krebs-Ringer bicarbonate medium did not appear essential for protein secretion. Amylase was secreted at a constant specific activity throughout an incubation of 3 hours when 78% of the enzyme and 53% of the total protein of the slice appeared in the medium. During early periods of incubation the amount of enzyme secreted into the medium was equivalent to the amount lost from the intracellular zymogen granules. Loss of amylase from the soluble supernatant fraction of the slice was observed only after the zymogen granules had released about 80% of their initial amylase content. The number of granules appeared to remain almost constant during secretion although their size and contrast was changed. It is therefore tentatively concluded that only the contents of the granules are transported out of the cell.